Coaxial cables and radio frequency switches that are used to leave a communications port open circuited are located inside the payload of a communications satellite and are usually well shielded. The center conductor of a coaxial cable connected to an RF switch may be electrically floating when it is not being used as a path for a RF signal.
The energy of electrons in a space environment is capable of causing the floating center conductor to charge to a high potential. When the cable is switched into a RF path, it is possible to induce a transient pulse from the floating center conductor onto a circuit in the RF path. The problem is that the induced pulse may cause damage to the electronics and in particular to sensitive monolithic microwave integrated circuits (MMIC) in the RF path.
To avoid this potentially serious problem, it is possible to insert coaxial attenuators having a low attenuation value into the paths that are susceptible to the transient pulse. However, this technique takes up valuable space due to the need for more cable roughing space, thereby adding unwanted weight to the spacecraft. In addition, the technique adds insertion loss, which is also undesirable.
It is also possible to continuously monitor space weather in order to determine optimum conditions for switching RF switches. RF switches are temperature dependent and simply waiting for the center conductor current potential to drop to a satisfactory level may be enough to prevent transients from entering the RF circuit. However, the monitoring method is extremely costly in that continuous, real-time space weather monitoring is required. Furthermore, scheduling problems arise because, say at 20.degree. C., it could take up to four days for the center conductor potential to drop to a satisfactory level. The scheduling problems adversely affect customer revenues due to the fact that the switches may be out of commission for an extended period of time.
According to flight data the probability of damage to sensitive electronic circuits during the switching process is low. However, should it occur, the effects could be extremely costly. Therefore, what is needed is a low cost method for preventing potential damage to sensitive electronic components without adversely affecting weight, and without occupying very limited, and very valuable, space onboard a spacecraft.